Painting Bridges: Chemical Stress In A Running Injury

Stay the CourseI use a lot of analogies in my clinical and coaching practices. No doubt, they’re entertaining for me, but I also feel they’re useful for making complicated processes easier to comprehend. What follows is one of my favorite analogies for what I believe is the principal factor in running injury.

“Why do we paint bridges?”

It sounds like a trick question, and I love asking it to my clients, especially my runner kids. And unless you’re a structural engineer, it’s a fun brainteaser. But before revealing the answer, let’s talk about steam engines. Yep, another analogy, so hop on board.

Get Going and Keep Going: Hormones that Drive High-Intensity Exercise

Hard running and our body’s fight-or-flight response are very similar. They are both fueled, in varying degrees, by powerful nervous and hormonal systems.

When we decide (either with the fire of a starter’s gun, or the firing of a real gun!) to take flight, two hormonal systems play a crucial role in getting and keeping us moving:

  1. Very-fast-acting ‘adrenaline’ (epinephrine, norepinephrine). These hormones instantaneously amp every part of our body to get us immediately moving to save our life. In athletic terms, this is the sprinter gear of our survival response. Go now!
  2. Less fast cortisol. This is another hormone secreted from the adrenal gland during a stress response. It helps keep us moving, supplementing the fast-acting flight systems with the energy they need to keep going. This is the marathon-gear survival. We are still going hard, more slowly, but for much longer.

For a more thorough primer on adrenal glands, their hormones, and function, consult Dr. Pam Smith’s piece on ‘adrenal fatigue.’

The Steam-Locomotive Analogy

A crude analogy of this high-intensity fight or flight: imagine the human body as a fire-fueled steam locomotive. In a resting state, the locomotive puffs along gently, burning a stable fuel of bulky slow-burning logs (in this analogy, fat) with relatively little necessity for fast- and hot-burning coal (glucose, carbohydrate).

But when called into flight–be it during a hard workout or race, or in a real survival situation–that locomotive’s engine must blast off with maximal energy to rapidly speed away.

The ‘conductor’ (the brain) immediately signals to the ‘engineers’ (the sympathetic nervous system and endocrine systems) to stoke the engines. They instantaneously message the ‘fireman’ to say, “We need fuel!”

The fireman’s first tool is adrenaline, which opens and activates all energy systems for full steam ahead. Fast-acting adrenaline, among other things, signals the consumption of any and all glucose for the getaway. Adrenaline powers the fireman’s shovel to fill the firebox with coal.

This rapid response, which happens in fractions of a second, creates enormous potential energy for action, which is paramount for our survival. That super-fast, intensely-hot-burning system powers immediate and swift action. Yet, this super-high-intensity response is inevitably short-lived. There’s only so much coal to shovel, ‘til it runs out. And like a race, we can’t sprint for very long.

But what if our flight is prolonged?

Glucose, that fast-burning coal, is in short supply. And those big ol’ logs (fat)? Too slow-burning to keep up the survival gear. In this case, the conductor has other tools. Through the engineers, the conductor signals the fireman to use cortisol. Through cortisol, the fireman is able to stoke the fire with alternative fuels. This, in effect, is the engine’s reserve energy system. While still powerful, as you’ll see, it is make-shift and wrought with potential negative effects.

Cortisol: The ‘Kitchen Sink’ Energy System

Physiologically, cortisol is a second-level stress hormone that provides additional back-up energy through catabolic energy liberation. In short, what cortisol does is break down other structures for use as fuel. It scrapes up alternative glucose from various sources, including:

  1. From glyocogen. Splits these long strains of carbohydrate into fast-acting glucose for energy.
  2. From fat. Breaks down triglycerides (fat storage) into free fatty acids, which eventually produces more energy.
  3. From muscle. Protein fibers in muscle are broken down into amino-acid building blocks, which are further reduced to produce more energy.
  4. From other byproducts. In the liver, other metabolic byproducts (lactate, glycerol) are also used to create energy.

As you can see, that’s a lot of breaking down! It’s akin to the fireman going through the train, ripping down wooden shelving (proteins), the upholstery (fat), and even the trash (lactate) and throwing it into the fire. In effect, cortisol powers the kitchen-sink fuel whereby the body breaks down essentially every physical structure for burning!

Through cortisol, we’re pretty much “cooking our garbage!” But its effects don’t end there. So severe are the orders from the engineer that most other non-essential operations are also halted. General upkeep and repairs (soft- and bony-tissue healing) and custodial and sanitation work (the immune system) are put on hold. This is to commit all resources for fueling the engine. And while this is a powerfully effective system for stoking a hot-burning engine–tearing apart the train to keep it going and ignoring repairs and sanitation–it is only a short-term option that, if too prolonged, will invariably result in catastrophe!

Even for a writer known for drawn-out analogy, that’s quite a yarn. The most important takes-away are these:

  • Cortisol is a second-level hormone that is activated by moderate- to high-intensity stress. These can be both real–like races, hard workouts, long runs, heavy strength training, and any moderate- to high-intensity exercise including non-impact cross training–or perceived–such as psychological or emotional stress (work, relationship, family stress).
  • Cortisol helps prioritize survival by mobilizing fast-acting fuels, producing an ongoing (and, on the short-term, inexhaustible) source of fuel.
  • In that process, cortisol breaks down key structural elements (muscles) for fuel.
  • To save resources for exertion, it curtails any tissue healing (muscle, bone) and immune-system function.

Based on these points, it is clear that, like many physiological processes, cortisol is a powerful, vital, and useful in the short-term but dangerous if utilized for too long. This, in effect, is the chemical stress of exercise.

Mediators of Cortisol: Balanced Stress and Rest

The good news is that cortisol can be limited in both frequency and intensity of use. Consistent and lower-intensity exercise helps down-modulate cortisol. In effect, by doing a lot of lower-intensity exercise, the body learns to more judiciously use its slow (logs) and fast (coal) fuel without resorting to tearing apart the train’s passenger seats for fuel.

Another huge mediator of cortisol is sleep. Sleep, in this crude analogy, has a way of calming the nerves of the conductor and engineer. Physiologically, the nervous system controls exercise and consumes by far the most fuel during heavy exertion (indeed, the brain itself consumes 25% of blood flow at all times). Thus, if the brain (conductor) and nerves (engineers) are properly rested, the conductor will find it far less necessary to dump cortisol into the system, thus preventing that panicked burn-it-all response. Sleep increases restoration and resilience throughout the body. More sleep, less stress.

After sleep, balanced training is the most important mediator of cortisol. As I tell my high-school kids, training is convincing the brain that what you’re doing is safe. In this way, we do large volumes of easy running to train our internal systems to do more running with less internal stress. This includes promoting fat-burning fuel (slower burning, but more abundant and less stressful) and decreasing quantities of destructive kitchen-sink fuel strategies.

This is the driving force behind the maxim of keeping the easy days easy. According the at least one study, cortisol secretion is negligible at exertion levels at or below 40 to 50% maximum oxygen uptake (VO2Max). At this level, blood cortisol levels raise only 5%. But with higher intensities, cortisol levels increase sharply: +39% cortisol at 60% VO2Max, and +83% cortisol at 80% VO2max.

About 50% VO2max equates to 60 to 70% maximum heart rate. Interestingly, this intensity level also correlates with Phil Maffetone’s “Maximum Aerobic Function” heart rate, described in this article on the importance of low-intensity exercise in returning to running after injury. In essence, by exercising at a low intensity, you are training the brain that running is safe, limiting the destructive chemical breakdown that occurs from too much cortisol.

That said, bouts of very high-intensity exercise can have the same effect! That, too, is brain training. Doing (and then surviving) short bouts of very hard exercise also trains the brain that we don’t necessarily need to burn the kitchen sink.

However, the most important element in stress and rest is the balance. Cortisol has its power not necessarily in circulating concentration, but in duration. The longer the body is ‘bathed’ in cortisol, the more pervasive and powerful its effects. Therefore, the key to mitigating cortisol is to blast very hard workouts–which temporarily create very high cortisol levels–then immediately follow with very low-intensity exercise, during which cortisol is destroyed.

Stress and rest. Stress and rest.

Easy is Not the Absence of Hard: The Importance of Having a Metric for Easy Training

Because cortisol increases markedly with even moderate-intensity exercise, keeping base-training efforts truly easy is vitally important because it limits the production and concentration of cortisol.

Conversely, if we start to ‘grind’–to run or cross train at medium or medium-hard efforts–cortisol increases sharply, yet seldom are any specific training objectives addressed. For many runners, this may be the difference between 30 to 60 seconds per mile on an easy day. This is a double-barreled negative effect:

  1. Cortisol is elevated (50 to 75%, versus 5%), ‘bathing’ tissue in corrosive cortisol for prolonged periods.
  2. Unless this is race-specific pace, no specific training objectives are being addressed. (Read: it isn’t a workout.)

High cortisol for nothing is a quick way to sabotage training and health! Thus, simply running medium-hard too often is an insidious pathway toward bonafide overtraining. Therefore, having a metric for easy is crucial in limiting cortisol production. This could be using a heart-rate monitor or more intuitively with mindful breath control. A meaningful metric for ultramarathon runners would be running at all-day pace.

Keeping easy days easy limits cortisol. Its relative absence allows for unfettered structural (muscle, tendon, bone) restoration, optimal immune function, and maximal readiness for those meaningful hard workouts and races.

And life stress counts! Because fight or flight is an automatic response to perceived threats, high cortisol levels can result in the absence of heavy exertion. Any ire-raising situations can cause the body to secrete and maintain high levels of blood cortisol levels. The longer they circulate in our system, the longer and more pervasively they ‘bathe’ the tissues in chemical stress. The body perceives stress (and in effect, high cortisol), expressed as elevated heart rate. This piece on the inter-relationship between physical exertion and non-exercise stressors explains why such life stress matters. High stress of any kind equals high cortisol, elevated internal strain, and impaired training and recovery.

Chemical Stress is the Preeminent Reason for Orthopedic Running Injury

Several years ago, I saw a cable news program expressing outrage about how “millions of dollars are being spent to paint a bridge!” They were incredulous that so much money was used for such a seemingly superfluous project.

“You know why we paint bridges?” I ask my student-athletes? The answer is to prevent corrosion. Chemical stress weakens physical structures. And weakened structures fail under load. Unpainted bridges rust. And rusty bridges collapse.

Chemically weakened tissues fail under otherwise normal stresses. This concept is so often overlooked by everyone from the orthopedic specialist, to the coach, to the athlete. But it is a compelling reason for chronic and repetitive injury.

The hallmark signs of chemically sensitized, over-trained runners include:

  • Failure to heal from an injury in a normal time frame. Most soft tissue (and bone) injuries heal in two to six weeks. Persistent pain and failure to heal often results when an athlete cross trains too intensely. Chemical stress is irrespective to impact, so your super-hard pool-running session floods your system with just as much cortisol as a hard run. Poor life-stress management can also prevent healing.
  • Pervasive injury sensitivity. These runners hurt one tissue (say, the left Achilles), recover, only to hurt another area (say, right hip) in quick succession. Cortisol saturation is systemic: all tissues are corroded, weakened, and prone to failure.
  • Unusual (or severe) non-traumatic injuries. The demise of tissues typically thought of as extremely tough and resilient is often chemically driven. Non-traumatic fractures to thick, sturdy bones like the femur, pelvis, or vertebrae in runners are often chemically mediated. This can also occur with major tendon ruptures like the Achilles and patellar tendons.
  • Impaired immune system. Chemically sensitized, over-trained runners tend to frequently get sick.
  • Impaired weight management. Chronically high cortisol impairs fat metabolism, blocks peripheral sugar uptake (in non-fight-or-flight cells), and, over time, promotes fat accumulation and weight gain. This is a prime reason that runners can run a lot, yet fail to manage let alone decrease body fat. (For a compelling and detailed analysis on the hormonal theory of obesity, check out Obesity Code: Unlocking the Secrets of Weight Loss by Jason Fung, MD.)

Thus, the keys to sustainable training, injury prevention, and optimal health are inherently stress management:

  • Balanced training. Have a metric for (true, low-intensity, cortisol-limiting) easy training. Then go hard, but allow optimal easy days to recover.
  • Life stress management. Limit cortisol production from non-running sources like family, relationship, and work stress.
  • Promote rest. Sleep is everyone’s most potent performance-enhancing strategy.

I strongly feel that the sustainable solution will improve multiple areas of our lives. By balancing chemical stress, injury risk will drastically decrease, fitness will rapidly increase, body fat will drop, and energy and mood will improve.

Call for Comments (from Meghan)

  • Alright, two extended analogies, one article, what do you think about Joe’s argument as a whole for the role chemical stress plays in our running injuries?
  • The ever-elusive balance of stress and rest, how do you find it? How have you successfully found it in the past? And when have you failed to strike this balance?

References

Hill EE1, Zack E, Battaglini C, Viru M, Viru A, Hackney AC. Exercise and circulating cortisol levels: the intensity threshold effect. J Endocrinol Invest. 2008 Jul;31(7):587-91.

NseAbasi N. Etim, Emem I. Evans, Edem E. A. Offiong, Mary E. Williams. Stress and the neuroendocrine system: implications for animal well-being. American Journal of Biology and Life Sciences. 2013; 1(1): 20-26

Relationship between Percent HR Max and Percent VO2 Max – NCSF. Obtained 12/9/2017 from https://www.ncsf.org/pdf/ceu/relationship_between_percent_hr_max_and_percent_vo2_max.pdf.

Joe Uhan

is a physical therapist, coach, and ultrarunner in Eugene, Oregon. He is a Minnesota native and has been a competitive runner for over 20 years. He has a Master's Degree in Kinesiology, a Doctorate in Physical Therapy, and is a USATF Level II Certified Coach. Joe ran his first ultra at Autumn Leaves 50 Mile in October 2010, was 4th place at the 2015 USATF 100K Trail Championships (and 3rd in 2012), second at the 2014 Waldo 100K, and finished M9 at the 2012 Western States 100. Joe owns and operates Uhan Performance Physiotherapy in Eugene, Oregon, and offers online coaching and running analysis at uhanperformance.com.

There are 24 comments

  1. mwith

    Minor correction, you inadvertently said cortisol is secreted from the kidney. You may want to correct that. Really good overview article.

  2. rdavies05

    A very timely read for me as I impatiently rest through a persistent cold a week after a fantastic hard long run… makes a ton of sense and gives me great motivation to ensure enough truly easy days in the week. Thank you Joe!

  3. Emily

    Another minor correction – breakdown of free fatty acids does not produce more glucose. It produces acetyl-CoA, which enters the Krebs cycle to produce energy. This is the same way glucose is metabolized. Nice article though!

    1. Joe Uhan

      Thanks, Emily. You’re right: it’s really all about ATP generation (to propagate the analogy: “carbon to burn”), which is the outcome from Krebs and other metabolic cycles. We made some clarifications to that effect (more generally calling it “energy”).

  4. Quigley

    Thanks again for another very informative post! I really liked the painting the bridge analogy, although I must admit that I first thought of spray painting or tagging, with the simple answer of people spray paint bridges because it is fun! However, I found the locomotive analogy less effective. I would have loved a little more detail on the upholstery (fat), and the trash (lactate) without the distraction of the analogies. I found this point the most interesting: “In the liver, other metabolic byproducts (lactate, glycerol) are also used to create glucose” and would enjoy seeing more of a discussion in a future post.

    1. Joe Uhan

      Thanks, Q & B. For more “grown-up” approaches, consider doing some scholar.google searches of the literature on cortisol and exercise.

      Good stuff, but a bit too in-depth for the purpose of this article, which is saying: “Quit running medium-hard, because it’s ruining your running (and, potentially, your overall health)”.

      1. Quigley

        Thanks, Joe! That would have been a fantastic title for this article: ““Quit running medium-hard, because it’s ruining your running (and, potentially, your overall health).”

    1. Joe Uhan

      Patrick-

      Thanks for the message.

      It’s a funny thing, because “cortisol gear” (that 60-80% VO2Max) just happens to be *the ultrarunning gear*!

      We’re not advocating “not running” at that gear; rather, you need to consider that “grinder gear” a bonafide workout. As such, you need to run that “race pace run” for the Training Specificity…then follow it with legitimately easier runs (ala that 40-50% VO2Max) in order to clear the cortisol, and get a true recovery run.

      Trouble occurs when every run generates beaucoup cortisol.

  5. The Other Albert

    Hey Joe,
    The way I see it, cortisol levels and stress (physical or emotional) are usually correlated. But I’m not sure the literature agrees that elevated cortisol levels predispose runners to injury. Rather, cortisol could be used a marker of stress – it increases during or after periods of high stress and/or low energy availability. Much like creatine kinase indicates muscle damage, but it doesn’t cause muscle damage. It’s reasonable that injuries are more likely to occur when cortisol is elevated… because the athlete has experienced a lot of stress, not because of the presence of cortisol.

    If I skip breakfast, run a hard 10 miler and don’t eat anything the rest of the day – my blood cortisol is going to be elevated (relative to taking an easy day). Then I do it again the next day. So I’ve got plenty of blood cortisol after that. But the cortisol won’t kill me. Cortisol won’t cause my injury. The injury will be the result of physical stress and a calorie/nutrient deficit. Cortisol is irrelevant.

    My advisor in grad school believed elevated cortisol after training had the potential to enhance, not hinder, tissue repair. By mobilizing amino acids during and after training, they become available for repair where they’re needed.

    If you want to emphasize or demonize cortisol, training stress & cortisol are likely to be correlated. Sometimes high training stress is required for adaptation. Sometimes recovery should be emphasized. We’re just talking about managing stress, not cortisol.

    1. Joe Uhan

      TOA-

      Thanks for the comment.

      Here’s a cop-out: “all in moderation”:

      1. Cortisol is [likely] positively adaptive, both during and post-exercise. There’s theories out there –especially related to intermittent fasting — that says the sort of “stripping down” of tissues (ala protein destruction) targets the *weakest* tissues. This, of course, is then followed by hypertrophy/hyperplasia.

      2. The danger in cortisol is in sustained concentrations. This is also true for any other corticosteriod drug: “cortizone” (the gold-standard orthopedic anti-inflammatory) is wonderful for quick reduction in acute inflammation and facilitaiton of healing….yet, the effects of chronic steriodal use (ranging from cortizone to albuterol to PEDs) is well-known to have destructive properties.

      My grandmother-in-law (may she rest in peace) fractured her humerus by a fall from about two feel (onto carpet); a break that failed to ever heal. It was theorized both her fracture (and previous fracture history) as well as the non-union were linked 40+ years of heavy albuterol use.

      Thus:

      – Acute cortisol over two days isn’t any more damaging as “rain on a bridge” for two days.
      – “Bathe” that bridge in “acid rain”, mostly every day, for years, and that, indeed, is going to erode structural integrity to the point where “normal loading” = significant injury.

      (For more on “normal loading on abnormal tissue”, from the inaugural column: http://www.irunfar.com/2012/03/anatomy-of-a-running-injury-part-1.html)

      1. Pam

        I agree with you that the elevated cortisol is likely to (at least in part) be causative to tissue injury. It is well characterized as a catabolic steroid (breaks down tissue, rather than an anabolic which builds tissue) and medicinal use of cortisol-like steroids greatly increases the risk of bone fractures and tendon ruptures. However, albuterol is not a steroid and would not be the cause of your grandmother’s fractured hip. If she had severe asthma she may have been on an inhaled steroid as well, though other factors (osteoporosis, smoking history) would have to be considered before entirely blaming the medication.

  6. Jadan

    I would guess that the same premise applies to recovery from injury. How many people jump into an alternative aerobic exercise activity if they pick up a running injury? Often this will be on the bike or other weight supported machine, or swimming, and they often push it harder aerobically than when they run because they can (and they think they need to to maintain fitness). I have always had a suspicion that pushing yourself in this way actually increases the length of time it takes the injury to heal. Depending on the type of injury I prefer to walk during the recovery phase which as well as keeping weight down and the blood flowing, helps to maintain more of that all important core and mobility endurance but at a lower intensity. Although I’m not an ultra-runner I am still very strong for a 55 year old with 40+ years of running behind me and I always come back into running relatively fit from this approach. With injuries that won’t allow walking I would still suggest that a less intensive approach to non weight bearing exercise is required.

  7. RunningStressed

    Interesting about the overall emotional/life vs physical/training stress balance and the science behind it. I (like most others) have my fair share of emotional/work/life stress. However the physical stress of a good run/training session (especially after a tough day or week) seems to wipe away any emotional stress and not add to any ‘overall’ body/health stress. It seems to have a positive effect on rest and general wellbeing, at least in the short term, were the system is reset and balance restored. I’ve always wondered about the long term effects of burning both ends of the candle in terms of work/training and if it finally catches up with you. For now it seems to be doing more good than bad…

  8. Run GMD

    Joe

    Great post, Joe. Maffetone says health is the optimal function of the body’s several systems. But do you consider abnormally elevated and/dysregulated cortisol itself and injury or is that just a precursor to injury? If an injury in itself then aren’t many of us already injured long before we know/feel it?

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